Phase noise is a major noise that causes interference to a communication system in wireless communication, the phase noise comes from oscillators in a transmitter and a receiver of the communication system, and may seriously affect transmission of a multi-carrier signal, so in order to reduce the influence of phase noise on the multi-carrier signal transmission, phase noise compensation can be performed on a received signal at the receiver to thereby guarantee accuracy of transmission.
In the prior art, a phase-tracking reference signal is introduced at the transmitter, which tracks a phase change arising from phase noise using the phase-tracking reference signal, and then the receiver performs phase noise compensation on the received signal according to the phase change.
Specifically a multi-carrier signal transmission can include the uplink transmission and downlink transmission, and when in the downlink transmission, as illustrated in FIG. 1a, 61 and 60 at the top-right corner represent different port serial numbers, where ports of a phase-tracking reference signal occupy a sub-carrier, and each phase-tracking reference signal is transmitted consecutively in a sub-frame; and the transmitter (e.g., a base station) can notify via dynamic downlink signaling the receiver (e.g., a user equipment) of the number of ports for the currently transmitted phase-tracking reference signal, e.g., two ports for transmitting the phase-tracking reference signal, or one port for transmitting the phase-tracking reference signal.
Specifically when in the uplink transmission, as illustrated in FIG. 1b, P=40 to 43 at the top-right corner represent port serial numbers, where ports of a phase-tracking reference signal occupy a sub-carrier, and each phase-tracking reference signal is transmitted inconsecutively in a sub-frame; and the receiver (e.g., a user equipment) can notify via dynamic downlink signaling the transmitter (e.g., a base station) of the number of ports for the currently transmitted phase-tracking reference signal, e.g., four ports for transmitting the phase-tracking reference signal, or two ports for transmitting the phase-tracking reference signal.
Furthermore a phase-tracking reference signal is used when the transmitter transmits user data to the receiver, and can be transmitted only after being pre-coded.
In the solution above, the phase-tracking reference signal passes through the same channel as the user data and a corresponding Demodulation Reference Signal (DMRS). The phase-tracking reference signal is used for calculating a phase difference between channel estimation on a symbol including the phase-tracking reference signal, and channel estimation on a symbol including the DMRS, to thereby determine a phase change arising from phase noise for channel estimation compensation and data demodulation.
In a multi-antenna transmitting and receiving system, a transmitter includes a plurality of antenna elements or antenna ports. If these antenna elements or antenna ports have same phase noise (phase noise from the same phase noise source), then phase noise may be estimated and compensated correctly in the solution above. However if the antenna elements or the antenna ports in the transmitter have different phase noises, then there may be a plurality of phase changes over channels through which user data pass, and the different phase changes arising from the respective phase noises cannot be estimated in the solution above, so that channel estimation compensation and data demodulation cannot be performed correctly.
In view of this, it is desirable to devise a method for transmitting a reference signal, and a method for determining phase noise so as to address the drawback above.